Improved fuel economy may be realized by deactivating part of the cylinders of a multi-cylinder engine and having the remaining cylinders carry the desired load. The primary reason for the fuel economy savings is that the working cylinders operate at a higher specific loading and therefore greater manifold pressure, which results in reduced intake stroke pumping work.
Multi-cylinder engines capable of cylinder deactivation have been produced. Typically, in the case of an in-line 4 cylinder engine, two cylinders are deactivated; in the case of a V-6, three cylinders (one bank) are deactivated. In both cases, cylinder deactivation is effected by disabling both intake and exhaust valves by using individual valve controllers. This causes the piston to compress and expand the trapped mass within the cylinder each revolution of the crankshaft, thereby creating a gas spring. That is, the trapped mass of gas is alternatively compressed and expanded. Engine operation according to this method is shown in FIG. 3 of this specification. Beginning at top dead center location which is noted "TDC" at the point of ignition ("IGN"), the pressure within the cylinder decreases from a super-atmospheric level down through atmospheric during the expansion stroke and ultimately decreases to a sub-atmospheric level at bottom dead center ("BDC"). Then the piston begins its upstroke, or exhaust stroke, and pressure ultimately builds to the same maximum at TDC at overlap ("O/L"). Then, expansion to a sub-atmospheric pressure occurs during the intake stroke as the piston moves down again to the position of BDC and thereafter rises during the compression stroke to TDC of ignition. Because the piston merely compresses and expands the gas which is trapped in the cylinder, the friction and thermodynamic losses are relatively small and the other engine cylinders, which are actually firing, may be operated with sufficiently greater efficiency so that the overall efficiency of the engine is improved. Neglecting heat transfer and piston ring blowby losses, the work done on compression is recovered on expansion so the only work expended is the friction for sliding the piston/ring assembly in the cylinder bore and the connecting rod bearings. And, the mechanical friction of the deactivated cylinders is reduced due to significantly lower peak cylinder pressures. Unfortunately, prior art systems which disable both intake and exhaust valves of an engine's cylinders are quite expensive and are therefore unattractive, because vehicles in which fuel economy is most important are frequently sold in the lower price range, and are therefore unable to command a price sufficient to offset the cost of the added equipment.
A previously filed U.S. patent application (Ser. No. 08/407,523) now U.S. Pat. No. 5,467,748 by the present inventors discloses cylinder deactivation using a wide-range exhaust-only camshaft phase shifter with port throttles. The present invention uses wide range intake and exhaust camshaft phase shifting but does not require port or plenum throttles to work as does the previous invention. The system according to the present invention may have a lower cost because it simply employs an actuator mechanism to phase shift the intake and exhaust camshafts equally on the cylinders to be deactivated. If the valves on the deactivated cylinders are controlled by a single overhead camshaft then the phase shifter is connected to the single camshaft. If the valves on the deactivated cylinders are controlled by dual overhead camshafts, one for the exhausts and one for the intake, then the phase shifter would control both camshafts equally either by providing two phase shifters, one for each camshaft, or a single phase shifter provided that, in the single phase shifter case, the two camshafts are mechanically linked together. Thus, according to the present invention, adjusting the timing of the valve lift events has no effect on the relative timing between the exhaust valve lift event and the intake valve lift event. That is, the timing between exhaust valve and intake valve lift events remains constant, regardless of phase shifting.
Accordingly, an advantage of the invention is to provide a system for cylinder deactivation in order to realize improved fuel economy.
Another advantage of the present invention is to provide a system for lowering peak cylinder pressure in a deactivated cylinder thereby reducing friction, heat transfer and blowby losses.
Still another advantage of the present invention is to provide a lower cost system for cylinder deactivation which employs a mechanism to phase shift the intake and exhaust camshafts equally on the cylinders to be deactivated.